Heretofore, silicon dioxide, that is SiO.sub.2, was generally incorporated into a rubber such as styrenebutadiene rubber either by direct mixing of solid silicon dioxide with the rubber polymer as in a Banbury, an internal mixer, etc., or by adding the solid SiO.sub.2 to a latex containing styrene-butadiene rubber and coagulating the mixture. However, direct mixing as in a Banbury was generally difficult and required multiple steps to incorporate significant amounts of silicon dioxide. Regardless of the number of steps, complete incorporation was not obtained and dusting was always a serious problem. Moreover, a large continuous mass was obtained and required grinding to achieve particles. Incorporation of amounts of silicon dioxide in excess of 50 percent by weight was generally difficult to achieve. The coagulation method of drying the product utilized a coagulant salt such as sodium chloride, calcium chloride, aluminum sulfate, magnesium sulfate, or a quaternary amine compound, and the like and also resulted in only part of the silicon dioxide being incorporated in the rubber. A further problem of the coagulation method is that the end product is a mass of rubber crumbs and hence must be subjected to a subsequent grinding operation. Regardless of method, fine-sized particles were not obtained.
U.S. Pat. No. 4,771,092 to Ollenik et al relates to a process for the production of free-flowing rubber powders with silicic acid as filler comprising combining a rubber latex with silicic acid filler while stirring in the presence of specific auxiliary agents, adjusting the pH range of the mixture to cause coagulation, and separating and drying the resultant solids wherein the specific auxiliary agents comprise organic surfactants together with colloidal silicic acid.
U.S. Pat. No. 4,757,101 relates to a process for producing a free-flowing silicic acid-filled powdered elastomer wherein the silicic acid has various properties such as (a) SiO.sub.2 : about 2 to 91.5 percent by weight; (b) metallic oxides: about 0.5 to 3 percent by weight; (c) loss on ignition (DIN 55 921/2 - measured at 100.degree. C.): about 8 to 15 percent by weight; (d) moisture (DIN 53 198 measured at 105.degree. C.): about 8 to 15 percent by weight; (e) surface area of the primary particles according to BET: about 40 to 250 m.sup.2 /g; (f) dibutyl phthalate absorption (ASTM D 2414-79) based on measured weight: about 170 to 290 percent; (g) linear average of numerical distribution of secondary particles: about 10 to 2,000 nm; (h) linear average of volume distribution of secondary particles: about 3 to 30 um; and (i) proportion of secondary particles with a diameter of less than 1 um: about 0.01 to 5 percent by weight.
U.S. Pat. No. 4,632,958 to Eshbach et al relates to a process for preparing pulverulent nitrile rubber particles which can be utilized to form high tensile strength materials, comprising co-precipitating, via the use of an aluminum cation as a co-precipitating agent, nitrile rubber latex and a silicate from an aqueous suspension wherein the suspension has a temperature within the range of from about 0.degree. C. to about 50.degree. C. and a pH ranging from about 7 to about 10.
U.S. Pat. No. 3,849,363 to Engel et al relates to a homogeneous rubber-silica mixture which is obtained by a common precipitation of a synthetic rubber latex and an alkali metal silicate solution with an acid.
U.S. Pat. No. 4,212,918 to Marquisee relates to a non-tacky elastomeric-shaped object by bringing shaped bodies of a normally tacky, uncured elastomer into contact with an aqueous bath containing a soluble coagulating salt for the latex, and a silicic or aluminic acid polymer, and washing and drying the resulting coated shaped objects.